Sea slugs are weird. But their sexual habits are even weirder. Take Chromodoris reticulata for example. It's a "simultaneous hermaphrodite," meaning it has both male and female sexual organs which it uses at the same time when mating (making it the envy of the animal kingdom). Even stranger, however, is how its penis detaches after copulation. But not to worry — a new penis grows back within 24 hours, a parlor trick Chromodoris can perform up to three times.

The study, which appears in Biology Letters, is appropriately titled, "Disposable penis and its replenishment in a simultaneous hermaphrodite" and was authored by Ayami Sekizawa, Yasuhiro Nakashima and colleagues. Writing in the paper, the Japanese researchers described the behavior as "extremely peculiar," adding that "No other animal is known to repeatedly copulate using such ‘disposable penes'."

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During sex, two sea slugs join together and connect their junk in all the right places. They proceed to both give and receive sperm. But after the mating takes place, the sea slug ejects its thread-like organ. The researchers theorize that, because the sea slug penis has backward pointing spines, it's difficult to withdraw it after copulation. So instead, it just gets rid of it. The shape of the penis may have something to do with its ability to remove the sperm from rival sea slugs.

As for Chromodoris's regenerative powers, the scientists noticed that a long portion of its penis is coiled up in a spiral inside its body, which it extends to replace the lobbed-off part.